Check valve assembly

ABSTRACT

A check valve assembly for use in a drill string to prevent reverse flow of drilling fluid through the string while permitting such fluid to be pumped downwardly through the well under normal conditions. The assembly includes: a valve body; a ball valve member, normally located out of the flow path in a side recess; a valve seat located above the valve member and means for controlling the rate of reverse flow of fluid required to move the valve member out of the side recess and against the valve seat.

United States Patent 1191 Brown [4 Nov. 26, 1974 [5 CHECK VALVE ASSEMBLY3,584,645 6/1971 Radig 166/224 x [75] Inventor: Cicero C. Brown,Houston, Tex. FOREIGN PATENTS OR APPLICATIONS 73 Assignee; Brown onTools, Inc" Houston 537,849 1/1956 Italy 137/5195 Tex. PrimaryExaminer-Robert G. Nilson [22] Flled: 1973 Attorney, Agent, orFirm-Torres & Berryhill [21] Appl. No.: 322,226 [57] ABSTRACT 52 us. c1137/271, 137/460 137/519.5 A check valve assembly for use in a String toP 166/224 175/318 vent reverse flow of drilling fluid through the string51 1m. 01 F16k 15/04 While Permitting Such fluid be Pumped dwnwardly[58] n w of Search n 137 /5 5 460 461 through the well under normalconditions. The assem- 6 2 /318 bly includes: a valve body; a ball valvemember, normally located out of the flow path in a side recess; a [56]References Cited valve seat located above the valve member and meansUNITED STATES PATENTS for controlling the rate of reverse flow of fluidrequired to move the valve member out of the side re- "gggard Cess andagainst the vaive seat 3,332,497 7/1967 Page 137/5195 X 9 Claims, 12Drawing Figures Pmzmm ve 3,850,191

SHEET 1 OF 4 CHECK VALVE ASSEMBLY BACKGROUND OF THE INVENTION 1. Fieldof the Invention The present invention relates to means for preventingreverse fluid flow through pipe. More specifically, the presentinvention relates to a check valve assembly suitable for employment in adrill string in which drilling fluid or mud is being pumped downwardlythrough the string. The assembly is designed to prevent upward flow ofthe drilling fluid when the drill bit enters a high pressure area.

2. Description of the Prior Art When drilling a well, there may arise aneed for a device to prevent the uncontrolled upward flow of thedrilling fluid or mud in the drill string, e.g., if the drill bit entersa high pressure area. Under normal operating conditions, the diviceshould allow unrestricted downward flow of the mud.

The prior art has suggested a number of valve assemblies designed toallow fluids or fluent materials to be pumped down through a drillstring and to prevent re verse or upward flow therethrough. See, forexample, U.S. Pat. Nos. 1,577,740 and 1,790,480. If the valve elementsare directly in the flow stream, the materials pumped down through thedrill string may erosively wear the valve components, particularly whensuch materials carry abrasive particles.

Previous check valve devices have employed a ball valve member and aseat member, along with a retainer or cage assembly. In these devices,the valve assembly is located directly in the flowstream and, therefore,subjected to the erosive action of abrasive material in the fluid. Suchvalves also restrict the downward flow f0 fluid and, with the valveassembly located directly in the flowstream, it is impossible forequipment to be lowered through the drill string past the assembly.

During drilling operations, the drill string may frequently be removedfrom the bore for maintenance of the drill bit. The valve assemblyshould allow fluid to empty from the drill string when it is raisedfrom-the bore. It is preferable that the valve assembly also allow fluidto flow at a predetermined rate upward past the assembly when the drillstring is being lowered into the well bore. By allowing the drill stringto fill from the bottom, fluid does not have to be pumped in at the topto lower the drill string and to prevent the drill string fromcollapsing because of pressure differentials. Valve assembliespreviously used, either allow no reverse fluid flow, or a predeterminedamount of flow at all sleeve for displacing the ball from the sidepocket when the differential pressure is increased sufficiently.

SUMMARY OF THE INVENTION The present invention provides a new andimproved drill string check valve assembly with an unrestricted flowpath which allows unrestricted downward flow and passage of flowlineequipment; but, which is provided with a means for regulating the rateof reverse flow so that the drill string can be lowered into the wellbore without having to pump fluid into the top of the drill string. In apreferred form of the invention, a tubular housing is provided, having arecess in its wall, for normally retaining a ball valve closure memberout of the flowstream Thus, the ball itself doesnt restrict the downwardflow of fluid and is protected from erosion by abrasive material in thefluid. The ball recess may communicate with the lower central bore ofthe tubular housing, via a pressure equalizing passage, which has anorifice bushing that can be changed to regulate the reverse flow rate.

Another advantage of the present invention is its simplicity of designand construction. It doesnt require special machining or specialcastings as in previous designs. Furthermore, the design is such thatthe assembly doesnt have to be completely removed from the drill stringwhen maintenance is required.

The foregoing and other features and advantages of the present inventionwill be more fully understood from the following specifications, claimsand the related drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical elevation,partially in section, schematically illustrating the check valveassembly of the present invention employed in a drill string;

FIG. 2 is an enlarged vertical cross section illustrating a preferredembodiment of the check'valve assembly of the present invention showingthe assembly in an open position;

FIG. 3 is a view similar to FIG. 2, illustrating the check valveassembly in a closed position;

FIG. 4 is an enlarged cross-sectional vertical elevation illustrating analternate embodiment of the check valve assembly of the presentinvention in an open positimes. The valve that allows fluid to flow allthe time is I undesirable. Such a valve works fine when lowering thedrill string into the well bore; but, when the drill bit enters a highpressure area, the flow can never be completely stopped.

Other devices have been designed to control only the upward flow f0fluid in well tubing and are not designed for use in a drill string,where fluid is allowed to flow in both directions. These devices areused in production strings to shut off the flow of oil when damageoccurs to equipment at the wellhead. See, for example, U.S. Pat. Nos.3,269,463; 3,332,497; 3,332,498; 3,411,585; 3,568,768; 3,584,645; and3,662,824. Many of these devices have a ball valve located in a sidepocket out of the flow stream and a movable inner tion;

FIG. 5 is an enlarged cross-sectional vertical elevation illustratinganother alternate embodiment of the check valve assembly of the presentinvention in the open position;

FIG. 6 is an enlarged cross-sectional vertical elevation illustratinganother alternate embodiment of the check valve assembly of the presentinvention in the open position.

FIG. 7 is an enlarged cross-sectional vertical elevation illustratingstill another alternate embodiment of the check valve assembly of thepresent invention;

FIG. 8 is a vertical elevation, partially in section, schematicallyillustrating an embodiment of the check valve assembly of the presentinvention employedin a drill string;

FIG. 9 is an enlarged vertical cross-section illustrating, in moredetail, the alternate embodiment of the check valve assembly shown inthe drill string of FIG. 8.

FIG. is a horizontal cross-section, taken along line 1010 of FIG. 9,illustrating the construction of the collar assembly of the assembly ofFIG. 9;

FIG. 11 is a view similar to FIG. 9 illustrating the check valveassembly in the closed position; and

FIG. 12 is an enlarged partial section further illustrating a retainerpin for the check valve assembly of FIG. 81 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a well, designated atA, employs a drill string check valve assembly indicated generally at10. A casing 11 is set in the well A in the usual manner. A drill bit 12is lowered into the well A through the casing 11 on a string of drillpipe 13. The check valve assembly 111 may be threadedly fastened to theend of the drill string 13 and also to the drill bit 12 by an adaptorfitting 14.

The assembly 111) comprises a body 15 and a central bore 16, throughwhich fluid is allowed to flow unrestricted in a downwardly direction.If flow is reversed and increased to a predetermined rate, a valve ball17 is displaced from a recess 18 in the body 15 into the bore 16 andlifted vertically by the fluid flow into engagement with a valve seatassembly 19 which completely stops the reverse flow. Although FIG. 1illustrated the assembly 10 as being connected adjacent to the drill bit12, it is not necessary that it be located in that position. It ispossible for the assembly 10 to be placed at any joint along the drillstring 13.

Refering now to FIG. 2 greater detail of the assembly 10 is shown. Asillustrated, the assembly 10 comprises the cylindrical body 15 and alongitudinal central bore 16, divided into three distinct sections; aconverging lower frusto-conical bore 20, a restricted cylindrical boreor throat 21, and an expanded upper cylindrical bore 22.

Female threads 30a and 30b located at each end of body 15 are used toconnect the assembly 10 to a drill string. Located at the upper end ofthe bore 22 is the valve seat assembly 19, having a valve seat bushing23 with a valve seat surface 23a. A resilient O-ring seal 24 encirclesthe bushing 23 and forms a fluid-tight seal between the bushing 23 andthe body 15. To allow for replacement of the bushing 23 and to maintainthe correct positioning, an externally threaded lock nut 25 ispositioned above the bushing 23.

The ball recess 18 is inclined and projects into the central restrictingbore 21 to form a ball guide 26. A cover plate 27 may be welded to thebody 15 to cover the recess 18 and to allow access to the ball 17.

A pressure equalizing passage 28 is located in the body 15 between therecess 18 and the frusto-conical bore 20. Located in the passage 28 isan externally threaded orifice bushing 29 with a cylindrical bore ororifice 29a. The positioning of the passage 28 may be such as to allowremoval of the orifice bushing 29 from the lower frusto-conical bore 20.It is the size of the orifice 29a in the bushing 29 which determines thereverse flow rate permitted.

During drilling operations, fluid is pumped down the drill string 13through the bore 16 and out the drill bit 12. The fluid assists themechanical cutting action of the drill bit 12 and returns cuttings tothe surface of the well. Also, when the drill string 13 has to beremoved from the well bore, the hydrostatic pressure of the fluid willseal the well bore.

When drilling resumes, after removal of a drill bit, the drill string 13must again be lowered into the well bore. The drill string 13 can belowered by gravity, until the weight of the fluid displaced by the drillstring equals the weight of the drill string 13. It is then necessary toeither pump fluid into the top of the drill string 13 to increase theweight, or to have a valve assembly, such as the one described herein,to allow the drill string 13 to fill from the bottom. Therefore, it isdesirable to have a check valve assembly with reverse flow capabilitieslike the assembly 10. But, the reverse flow rate must be regulated sothat when the drill bit 12 enters a high pressure area, the valve willcompletely close and prevent reverse flow of fluid.

If the pressure below the drill bit 12 is greater than the pressure inthe drill string 13, the fluid will start to flow upwardly through thedrill string 13. When the reverse flow reaches a predetermined rate, theball 17 will be displaced from the recess 18 into the bore 22 and thefluid will force the ball 17 into contact with the seat surface 23a. Theball 17 is displaced because of a pressure differential created betweenthe recess 18 and the restricted central bore or throat 2]. Thispressure differential exists because the entire hydraulic head withinthe recess 18 is in the form of pressure energy, whereas the samehydraulic head in the throat 21 is partially in the form of kineticenergy embodied in the fluid flow. The pressure at the throat istherefore lower than that in the recess 18. This is in accordance withthe well established principle outlined in hydraulic textbooks, e.g.,Fluid Dynamics by Daily and I-Iarleman (Adeison-Wesley 1966), and whichis expressed quantitatively by the well known equation of Bernoulli.

When the orifice bushing 29 is blanked off so as to allow nocommunication of pressure through it, the initial pressure differentialacting on the ball 17 will be at a maximum. However, if an orifice 29ais fitted in the bushing, some reduction of pressure will take place inthe recess due to this communication. The larger the bore 29a the higherthe flow rate which will cause the ball 17 to be displaced from recess18 into bore 22 and to be forced upwardly into engagement with valveseat surface 23a, as illustrated in FIG. 3.

Subsequently, when the pressure below the valve assembly 19 becomes lessthan the pressure above, the ball 17 will drop down the bore 22 to guide26 and will be diverted back into the recess 18 because of the gravityacting on the ball 17 and the reduced diameter of the throat 21, whichis insufficient to pass the ball. The passage 28, or the clearancebetween ball 17 and recess 18, will allow the fluid displaced by theball 17 to escape from the recess 18. When the ball 17 has returned tothe recess 18, the drilling process can be resumed.

FIG. 4 refers to another form of the drill string check valve assemblyindicated generally at 110. The construction and operation of theassembly 110 is basically the same as that of the assembly 10 in FIG.1-3. Therefore, to avoid repetition of description, the referencenumbers for similar components in the assembly 11(1) have added to thereference number of corresponding components in the assembly 1(1). Thebasic difference of the assembly is that it comprises three sections; abody 115, a sleeve 127 and a collar 131; instead of the single body 15of FIGS I-3. The sleeve 127 is removable to facilitate access to theball recess 118 and also the passage 128 so that the ball 117 andorifice bushing 129 can readily be replaced. The collar 131 isthreadedly fastened to the upper portion of the housing 115 andmaintains correct positioning of the sleeve 127. Encircling the body 115and the collar 131 are two resilient O-rings, 115a and 131a,respectively, forming a fluid-tight seal around the sleeve 127.

It will be appreciated that the replacement of the valve seat assembly119, ball 117, and orifice bushing 129 can be accomplished byunthreading the collar 131 from the body 115 and lifting the sleeve 127from the housing 115. In this form, only the upper joint 132 has to betaken apart to replace all components in the assembly 110.

Another modification of the invention, indicated generally at 210, isshownin FIG. 5. The assembly is referenced to the specifications ofFIGS. 1-3 by adding 200 to the reference numbers of correspondingcomponents of assembly 10. The assembly 210 is designed to respond morerapidly to a pressure increase.

A bore 232 is aligned with the pressure equalizing passage 228 andallows replacement of the orifice bushing 229. A blunt-nosed set screw233 may be used to plug the bore 232 and also to position the ball 217away from the cover plate 227. The ball 217 is placed nearer the bore221 than in the previously described embodiments. Therefore, thepressure differential needed to displace the ball 217 into theflowstream is lower and will result in faster action. Encircling the setscrew 233 is a resilient O-ring 233a forming a fluidtight seal betweenthe bore 232 and the set screw 233. Althugh such is not necessary, aconventional adaptor 234 designed to cooperate with a well loggingdevice is shown located above the valve seat assembly 219.

Referring now to FIG. 6, still another modification of the drill stringcheck valve assembly, indicated at 310, will be described. It consistsof a lower body 315, an upper collar 331, and a removable sleeve 327.The lower bore section 320 is cylindrical, instead of frustoconical asin previous modifications, FIGS. 1-5.

To assist in achieving the pressure differential, a slidable restrictingsleeve 335 may be located in the bore 320. To prevent the sleeve 335from exiting the lower bore 320, a snap ring 336 may be placed in agroove at the lower end of bore 320. In normal operation, the sleeve 335is forced into contact with the snap ring 336. When a reverse flowoccurs, the sleeve 335 will slide upwardly, being forced by the fluidinto position adjacent the central restricting bore 321. The additionalrestriction caused by the sleeve 335 will make the pressure differentialbetween the restricted bore or throat 321 and the lower bore section 320great enough to displace the ball 317 from the recess 318. Control ofreverse flow differential is determined by the size of the bore 337 inthe sleeve 335. Therefore, in this modification, it is not necessary tohave an orifice or orifice bushing in the passage 328.

With reference to FIG. 7, still another modification of the drill stringcheck valve assembly, generally indicated at 410, will be described. Inthis form, the body 415 contains a removable tubular insert 415ainserted in the bore 416. It will be appreciated that the insert 415a isthreadedly secured at 438, allowing its removal when replacement of thevalve seat bushing 423 is necessary because of wear on the seatingsurface 423a. The insert 415a contains bore sections 420, 421 and 422which create the Venturi effect necessary for displacing ball 417 fromrecess 418. The valve assembly 419 includes a bushing 423, O-ring 424,lock-nut 425, and ball return guide 426. A fluid-tight seal between thebody 415 and removable section 415a is formed by a resilient O-ring 439located in a groove 440 surrounding section 415a.

Referring to FIG. 8, still another embodiment of the invention is shownfor use in a well, generally indicated at W, having a casing C set inthe well W in the usual manner. A drill bit B is shown attached to drillstring S by an adaptor fitting F and lowered into the well W though thecasing C. The check valve assembly of the present embodiment isindicated generally at 510 near the surface in the drill string S.

As may best beseen by reference to FIG. 9, the assembly 510 includes abody 511, having a multi-section longitudinal bore 512, a valve seatassembly 513, and a ball valve 514 positioned out of the bore 512 in aninclined recess 515 in the body 511. A ball return guide 516 projectsfrom the recess 515 into the bore 512.

The bore 512 is designed to function as a Venturi, having a lowerfrusto-conical section 517, a lower cylindrical section 517 a centralrestricting section 518, and an enlarged upper cylindrical section 519which allows axial movement of the ball 514. Communicating between thefrusto-conical bore 517, lower cylindrical bore 517 and the recess 515is a pressure equalizing passage 518. A cover plate 519 may be welded tothe body to cover the hole made during the construction of the recess515 and the passage 518.

Located below a threaded box 520 in the upper portion of the body 511 isthe valve seat assembly 513 which includes a valve seat bushing 521having an annular seating surface 521a. A resilient O-ring 522 encirclesthe bushing521 to form a fluid-tight seal between the bushing 521 andthe body 511. An externally threaded lock-nut 523 maintains the correctpositioning of the valve seat bushing 521 and allows replacement of thebushing 521 when the seating surface 521a becomes eroded.

A tapped bore 524 communicates with recess 515 from the outside ofhousing 511. A lock pin 525 is dis posed in the bore 524 and held in amovable position by an externally threaded bushing 526. A resilient O-ring 527 encircles the pin 525 and forms a fluid-tight seal between thepin 525 and the bushing 526. To keep the ball 514 in the recess 515, aclamp assembly 528 may be provided for engagement with the housing 51 1and the end of pin 525 to compress a biasing spring 529 forcing the pin525 to protrude into the recess 515, as best illustrated in FIG. 12.FIGS. 9 and 10 illustrate the clamp assembly 528 after being installedin the drill string S of FIG. 8.

The clamp assembly 528 may be removed from the body 511, releasing thetension on spring 529 and allowing pin 525 to be retracted. Reversefluid flow will create a high pressure area in the bore 517' and recess515 and a lower pressure area in the bore 518. The pressure differentialwill displace the ball 514 from recess 515, since the pin 525 no longerprotrudes into the recess 515, and the ball 514 will move axially upwardinto sealing engagement with the valve seating surface 521a, as shown inFIG. 11. With the ball 514 seated in the seat 521a, the reverse flowwill be completely stopped. To return the ball 514 to its normalposition in recess 515, the pressure above the valve assembly 513 mustbe greater than the pressure in the bore 517. The pressure differential,as well as gravity, will then force the ball ll4 down the bore 519,guide 516 and into the recess 515.

Details of the construction of the removable clamp assembly 528 isillustrated in FIG. 10. The clamp assembly 528 includes a C-shapedbracket 530 and a stationary cylindrical handle 531 welded to thebracket 530. The handle 531 engages a notch 532 located in the body 511of the assembly 510. The second handle 533 is internally threaded forconnection with a threaded pin 533a. A spring 534 encircles the pin 533awithin a retainer socket 535 which has an opening to allow the threadedportion of the pin 533a to extend therethrough. The socket 535 is weldedto the bracket 530 and the handle 533 threaded onto the pin 533a. Theclamp assembly 528 is held in place by the biasing spring 534 whichforces the head of the pin 5330 to engage notch 536 in the body 511.

When the check valve assembly 510 is installed in the drill string S, itcan be made operative in response to reverse flow of fluid by removingclamp assembly 528. This can be accomplished by pulling the handle 533outwardly from the housing 511, compressing the spring 534 anddisengaging the pin 533a from notch 536. With the collar assembly 528removed, contact with the lock pin 525 is lost, and the biasing spring529 retracts the pin 525 from the recess 515, allowing the ball 514 tomove into the flow path and seat in the valve seat assembly 513.

The foregoing description has disclosed a unique check valve assemblyfor control of reverse flow in drill strings. Such an assembly isreliable and simple to manufacture. Although, several embodiments of theassembly have been described herein, the invention is not so limited.Various changes in the size, shape, and materials of the assembly, aswell as in the details of construction, may be made without departingfrom the spirit of the invention. For example, although it is preferablefrom the standpoint of control, it is not. necessary that the checkvalve assembly of the present invention be provided with an equalizingpassage such as 28 in FIG. 1. However, if there is no equalizingpassage, enough clearance must be provided between the ball closuremember and its recess to allow displacement of fluid from the recess orreturn of the ball from the closed position. It is therefore intendedthat the scope of the invention be limited only by the claims whichfollow.

I claim:

1. A check valve assembly for permitting unrestricted flow in onedirection and limited flow in the reverse direction comprising:

a. a valve body, having walls the exterior of which are cylindrical andsubstantially uniform in diameter throughout the length of said valvebody, said walls surrounding a longitudinal flowbore. comprising firstand third concentric sections connected by a second concentric sectionof restricted diameter;

b. seat means carried by said valve body at one end of said third flowbore section;

c. recess means in said valve body walls communicating with saidflowbore wear the junction of said second and third flowbore sections;

(1. ball closure means carried in said recess means out of said flowborebut movable into said flowbore for sealing engagement with said seatmeans, in response to a predetermined rate of reverse flow through saidcheck valve assembly, to block reverse flow of fluids through said checkvalve assemy;

e. equalizing passage means in said valve providing fluid communicationbetween said recess mean and said first flowbore section, saidequalizing passage being provided with replaceable orifice means,changing of which regulates the reverse flow rate to which said ballclosure member is responsive for blocking flow through said check valveassembly.

2. A check valve assembly as set forth in claim 1 in which said firstflowbore section is frusto-conical, converging toward said second andthird sections, which are cylindrical.

3. A check valve assembly as set forth in claim 1 in which said recessmeans is a cylindrical hole of a diameter slightly larger than thediameter of said ball closure member and whose axis intersects the axisof said flowbore at an inclined angle so that said cylindrical hole isinclined toward said third flowbore section.

4. A check valve assembly as set forth in claim 1 in which said first,second and third flowbore sections are carried in a tubular insertdisposed in a surrounding cylindrical section of said flowbore forremoval through the end of said valve body adjacent said first flowboresection.

5. A check valve assembly as set forth in claim 4 in which said seatmeans is attached to said tubular insert permitting replacement of saidseat means on removal of said insert from said surrounding section ofsaid flowbore.

6. A check valve assembly as set forth in claim 1 in which said valvebody is provided with an access port through which said orifice meansmay be externally removed from said check valve assembly, said accessport communicating with said equalizing passage through said recessmeans.

7. A check valve assembly as set forth in claim 6 in which said accessport is sealingly closed by plug means, said plug means projecting intosaid recess means for limiting the movement of said ball closure meansin said recess means.

8. A check valve assembly as set forth in claim 1 comprising a sleevemember surrounding aid valve body and retained thereon by retainermeans, said sleeve member being removable on removal of said retainermeans to permit access to said recess means.

9. A check valve assembly as set forth in claim 8 in which said orificemeans is replaceable through said recess means on the removal of saidsleeve member, for controlling the reverse flow rate to which said ballclosure member is responsive for blocking reverse flow through saidcheck valve assembly.

1. A check valve assembly for permitting unrestricted flow in onedirection and limited flow in the reverse direction comprising: a. avalve body, having walls the exterior of which are cylindrical andsubstantially uniform in diameter throughout the length of said valvebody, said walls surrounding a longitudinal flowbore comprising firstand third concentric sections connected by a second concentric sectionof restricted diameter; b. seat means carried by said valve body at oneend of said third flowbore section; c. recess means in said valve bodywalls communicating with said flowbore near the junction of said secondand third flowbore sections; d. ball closure means carried in saidrecess means out of said flowbore but movable into said flowbore forsealing engagement with said seat means, in response to a predeterminedrate of reverse flow through said check valve assembly, to block reverseflow of fluids through said check valve assembly; and e. equalizingpassage means in said valve providing fluid communication between saidrecess means and said first flowbore section, said equalizing passagebeing provided with replaceable orifice means, changing of whichregulates the reverse flow rate to which said ball closure member isresponsive for blocking flow through said check valve assembly.
 2. Acheck valve assembly as set forth in claim 1 in which said firstflowbore section is frusto-conical, converging toward said second andthird sections, which are cylindrical.
 3. A check valve assembly as setforth in claim 1 in which said recess means is a cylindrical hole of adiameter slightly larger than the diameter of said ball closure memberand whose axis intersects the axis of said flowbore at an inclined angleso that said cylindrical hole is inclined toward said third flowboresection.
 4. A check valve assembly as set forth in claim 1 in which saidfirst, second and third flowbore sections are carried in a tubularinsert disposed in a surrounding cylindrical section of said flowborefor removal through the end of said valve body adjacent said firstflowbore section.
 5. A check valve assembly as set forth in claim 4 inwhich said seat means is attached to said tubular insert permittingreplacement of said seat means on removal of said insert from saidsurrounding section of said flowbore.
 6. A check valve assembly as setforth in claim 1 in which said valve body is provided with an accessport through which said orifice means may be externally removed fromsaid check valve assembly, said access port communicating with saidequalizing passage through said recess means.
 7. A check valve assemblyas set forth in claim 6 in which said access port is sealingly closed byplug means, said plug means projecting into said recess means forlimiting the movement of said ball closure means in said recess means.8. A check valve assembly as set forth in claim 1 comprising a sleevemember surrounding said valve body and retained thereon by retainermeans, said sleeve member being removable on removal of said retainermeans to permit access to said recess means.
 9. A check valve assemblyas set forth in claim 8 in which said orifice means is replaceablethrough said recess means on the removal of said sleeve member, forcontrolling the reverse flow rate to which said ball closure member isresponsive for blocking reverse flow through said check valve assembly.